620 Produce Degradation: Reaction Pathways and their Prevention
Maturity at harvest and degree of ripeness are important factors in determining
chilling sensitivity in some fruits. The effects of chilling are cumulative in some
commodities, so that low temperatures in transit, or even in the field shortly before
harvest, may add to the total effects of chilling that occur in cold storage.
Variations in the effect of chilling injury on tissues are illustrated by the following
generalizations^31 :
- Some species are susceptible, whereas others are not.
- Within a susceptible species, some genotypes are more susceptible than
others. - Within a genotype, most, if not all, organs are susceptible, but some organs
are more susceptible than others. - Within an organ, response does not tend to be uniform and is often
localized. - Damage incurred at low temperatures may not become evident until the
plant or organ is exposed to nonchilling temperatures.
20.4.1.2 Symptoms
Although chilling of the growing plant may reduce its final yield, damage to produce
may appear if chilling occurs after harvest, during transport, or in storage. Some
symptoms of chilling injury are only skin-deep (spots, pits, or discoloration), but
others involve a more extensive breakdown of internal tissues that may be visible
only when the fruit is cut. In addition to the visible symptoms, chilled fruits tend
to be more susceptible to decay and may fail to ripen properly.
Some of the more common visual symptoms of chilling injury include the
following^28 :
- Surface lesions: pitting, large sunken areas, and discoloration
- Water-soaking of the tissues: disruption of cell structure and accompany-
ing release of substrate favors growth of microorganisms; this commonly
occurring symptom in leaves is followed by wilting and desiccation - Internal discoloration of pulp, vascular strands, and seeds
- Breakdown of tissue
- Failure of fruits to ripen in the expected pattern following removal to
ripening conditions - An accelerated rate of senescence, but with otherwise normal appearance
- Increased susceptibility to decay, especially to organisms not usually
found growing on healthy tissue - A shortened storage life or shelf life due to one or more of the above
responses - Compositional changes
- Loss of growth (sprouting) capacity
Figure 20.9 through Figure 20.14 show chilling injury in a variety of horticultural
products.